Tonometric catheter combination

ABSTRACT

A tonometric device for use in hollow viscus tonometry and remote sensing of patient fluid parameters is disclosed. The device is capable of monitoring certain critical fluid properties of interest, such as oxygen gases and carbon dioxide gases in the wall tissue itself of the patient&#39;s organ, rather than monitoring such properties in a lumen of the organ. A walled sampling chamber, which is preferably an inflated balloon member, is provided on an elongated tube, with provisions for positioning the sampling chamber in direct contact with a wall portion of the patient&#39;s internal organ.

This is a continuation of copending application, Ser. No. 496,186, filedMar. 20, 1990 (now abandoned), which is a continuation of anapplication, Ser. No. 380,704, filed Jul. 13, 1989 (now abandoned),which was a continuation of an application, Ser. No. 237,286, filed Aug.26, 1988 (now abandoned). This is also a continuation-in-part of acopending application, Ser. No. 513,026, filed Apr. 24, 1990 (nowabandoned), which was a continuation of an application, Ser. No.237,288, filed Aug. 26, 1988 (now abandoned), which was acontinuation-in-part of an application, Ser. No. 233,888, filed Aug. 17,1988 (now abandoned), which was a continuation of an application, Ser.No. 120,720, filed Nov. 6, 1987 (now abandoned), which was acontinuation of an application, Ser. No. 013,552, filed Feb. 11, 1987(now abandoned), which was a continuation of an application, Ser. No.833,287, filed Feb. 27, 1986 (now issued as U.S. Pat. No. 4,643,192),which was a continuation of an application, Ser. No. 360,718, filed Mar.22, 1982 (now abandoned).

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates to medical diagnostic equipment and methods andis particularly concerned with hollow viscus tonometry and remoteelectronic and optical sensing.

The prior art (see U.S. Pat. No. 4,643,192) has recognized thatintestinal ischemia, and to a lesser degree, stress ulceration, are twoproblems that plague physicians involved in the management of patientsin intensive care units. Intestinal ischemia, in particular, has aninsidious onset and may not be detected until days after the intestinehas become completely and irreversibly compromised. A delay in thediagnosis of intestinal ischemia may have devastating consequences for apatient. The availability of means for early diagnosis and management ofpatients with these problems would have immediate applicability in allintensive care units, especially where the procedure can be convenientlyconducted with reasonable safety and reliability.

It has been established that a fall in the intramucosal pH may precedethe development of intestinal ischemia and stress ulceration. As Ireported in my prior U.S. Pat. No. 4,643,192, expressly incorporatedherein by reference, entitled "Hollow Viscus Tonometry" a fall inintramucosal pH also occurs within minutes of inducing intestinalischemia in dogs. The fall in pH in intestinal mucosa, and hence thelikelihood of ischemia or stress ulceration, can be reliably calculatedfrom a pCO₂ (partial pressure of CO₂), or other indicia of pH, inluminal fluid and the bicarbonate concentration in arterial blood. Themethod of calculating the pH in intestinal mucosal tissue, pursuant toprinciples of my prior patent, has been validated by directedmeasurements under a variety of conditions simulating clinical problems.A correlation coefficient in the order of 0.92 to 0.95 has been obtainedin each of 16 dogs. The validity of the procedure is inherentlyextensible to humans, and indeed may also be useful in assessing thevitality of other hollow organs and tissue. See R. G. Fiddian-Green etal. "Splanchnic Ischemia and Multiple Organ Failure".

To measure the pCO₂ in the lumen of the gut it has heretofore beennecessary to obtain and remove a sample of fluid that has been incontact with the wall of the gut for a certain time period, usually atleast half an hour. It has now been observed that it is somewhatdifficult to manually aspirate the sampling fluid or medium from atonometric catheter located in the gut or other internal focus with anyconsistency. It is much easier to obtain such samples from the stomach,but samples obtained from the stomach frequently contain foreignmaterial that can damage a gas analyzer.

As taught in my prior patent, the desired sample or samples can beobtained from the gut using a catheter tube (called a tonometriccatheter) having a walled sampling chamber on the tube with the samplingchamber being in sample-specific communication with the hollow interiorof the tube. The wall of the sampling chamber comprises a material whichis substantially impermeable to liquid yet is highly permeable to gas.One suitable material is polydimethylsiloxane elastomer.

In use the catheter is introduced into a patient to place the samplingchamber at a desired site within the gut. An aspirating liquid or mediumis employed to fill the interior of the sampling chamber. The samplingchamber is left in place at the desired sampling site long enough toallow the gases present to diffuse through the wall of the samplingchamber into the aspirating liquid. The time should be long enough forthe gases to equilibrate. The liquid impermeable nature of the samplechamber wall material prevents both the aspirating liquid from leakingout of the chamber and also the intrusion of any liquids into theaspirating liquid. After the appropriate or desired amount of placementtime has elapsed the aspirating liquid is aspirated along with the gaseswhich have diffused into it. The sample thus obtained is analyzed forgas content, in particular for pCO₂. In this way the pCO₂ within thelumen of the gut can be reliably measured with the fluid being free fromlumenal debris.

In carrying out the diagnostic method taught in my prior patent the pCO₂measurement is utilized in conjunction with a measurement of thebicarbonate ion concentration (HCO₃ ⁻) in an arterial blood sample ofthe patient for determining the pH of the tract wall.

Depending upon the particular condition of a given patient, the cathetermay be left in place and samples may be taken at periodic intervals sothat pH values may be periodically calculated. The procedure has a highreliability in accurately determining the adequacy of organ tissueoxygenation, and diagnosing intestinal ischemia in its incipient stages.Such determination or detection can be useful in treating the patient sothat the potentially devastating consequences resulting from less timelydetection may often be avoided.

While the sampling techniques taught in my prior patent have providedhighly accurate and reliable results, it has now been observed thatthere are instances (in the care of the critically ill in intensive careunits, for example) in which remote sensing of the organ or organ-wallcondition and automatic calculation of the organ or organ-wall pH wouldbe advantageous and easier to effectuate. This method would thuspartially or totally eliminate the need for the somewhat cumbersomeaspiration of the sampling fluid or medium which fills the samplingchamber; it may also eliminate the need for the sampling chamber to bein sampling-medium communication with any other part of the device.There is also a need to extend the benefits of tonometric sampling andsensing to other internal hollow viscous organs. To this end, there is aneed for new and different tonometric devices specifically adapted toallow my sensing and sampling techniques to be performed with ease in aclinical environment, and in combination with other procedures.

The importance and significance of determining the pH of the wall of agiven hollow viscous organ has been recently dramatically magnified as aresult of the recent recognition that the pH of the wall of a givenorgan can be employed to accurately evaluate the vitality and/orstability of that organ as well as others; this is in contrast to merelydetermining whether such an organ is experiencing an ischemic event.Further, certain organs can be selected for monitoring, either alone orin combination, and evaluation of this organ or these organs can aid inpredicting the overall condition of the patient, or the onset of amultitude of pathologies, including predicting or identifying suchevents as multiple organ failure. Such a methodology can be employed togreatly enhance and supplement the monitoring of the critically ill, forexample.

In one aspect, the present invention provides a new apparatus and methodfor remotely sensing organ condition and conveying an electromagneticsignal, e.g. an electrical current or optical signal, to an electronicor optical apparatus located outside the organ under investigation. Inone embodiment, a chemically sensitive electronic transducer (orplurality of transducers), such as a field effect transistor, isattached to a tonometric catheter for introduction into the organ alongwith the tonometric catheter. The first electronic sensor, preferablynon-temperature, generates and conveys an electromagnetic signalindicative of some desired aspect of organ condition, e.g., indicativeof the pCO₂, pH and/or pO₂ level of the organ or organ-wall. Forexample, in one preferred embodiment, mean ambient pCO₂, pH and/or pO₂of lumenal fluid or the like is measured or monitored via wire or othersuitable electromagnetic energy conveying means to an electronic circuitwhich interprets the electromagnetic signal and produces a report of theorgan condition. The electronic circuit may include an input forreceiving a separately determined signal indicative of the blood pH ofthe patient. Using this pCO₂, pH and/or pO₂ measurement along with blood(preferably arterial) pH data, the electronic circuit determines the pHof the organ wall under test and thereby provides information fordetermining the organ's current condition or perhaps predicting theorgan's future condition. The electronic circuit may be suitablyconstructed from analog components, digital components or both.

In another embodiment, a pH, pCO₂ or pO₂ sensitive colorimetricsubstance is injected into an area adjacent to the organ, e.g., into thesampling chamber of the tonometric catheter, and an optical sensor isemployed to detect color change in order to determine the pH of the wallof that organ. The optical sensor can either be disposed in or on thetonometric catheter for introduction into the area adjacent the organ orit may be disposed outside the organ with fiber optic cable opticallycoupling the sensor to the tonometric catheter site at which the pHsensitive substance has been injected.

In another aspect the present invention provides a variety of new anddifferent tonometric catheter devices for sensing and/or sampling afluid or gas property (such as pH, pO₂, pCO₂, and the like) which isindicative of the condition of an internal organ, in conjunction orcombination with a walled catheter tube adapted for delivery or drainingfluids, such as nasogastric tubes, urinary catheters, uretericcatheters, intestinal feeding tubes, wound or abdominal drains (suctionor regular) and biliary tubes, catheters and stents, with or withoutremote sensing means for pH, pCO₂ and/or pO₂.

In still another aspect or embodiment, the device employs two separatewalled catheter tubes, one tonometric catheter tube for the measurementof a fluid or gas property, that is in communication with the samplingchamber; and a second walled catheter tube adapted for delivering ordraining fluids.

In yet another aspect or embodiment, the device employs a walledsampling chamber in communication with a sensing means, and a secondwalled catheter tube adapted for delivering or draining fluids.

Optionally, when a non-temperature sensing-means is employed, a secondsensing-means may be employed as well.

For a more complete understanding of the invention, its objects andadvantages, reference may be had to the following specification and tothe accompanying drawings. Also, see my co-pending and commonly assignedapplications filed of even date herewith entitled "Remote SensingTonometric Catheter Apparatus and Method" and "Hollow Viscus and SolidOrgan Tonometry", bearing respective Ser. Nos. 237,287 filed Aug. 26,1988 (now abandoned), and 237,288, filed Aug. 26, 1988 (now abandoned)both of which are totally and expressly incorporated herein byreference.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a first embodiment of the tonometric catheter;

FIG. 2A is a partial cross-sectional view of the tonometric catheterillustrating a first means for attachment of an electronic field effecttransistor sensor;

FIG. 2B is a partial cross-sectional view of the tonometric catheterillustrating a second means of attachment of the field effect transistorsensor;

FIG. 3 illustrates the method of use of the tonometric catheter inmeasurement of the pH of the colon and also of the stomach, the specificembodiment illustrated for colonic measurement being that of FIG. 5 andthe specific tonometric catheter for gastric measurement being that ofFIG. 4;

FIG. 4 is another embodiment of the tonometric catheter with nasogastrictube;

FIG. 4A is a cross-sectional view of the tonometric catheter of FIG. 4taken substantially along the line 4A--4A of FIG. 4;

FIG. 4B is a cross-sectional view of the tonometric catheter of FIG. 4taken substantially along the line 4B--4B of FIG. 4;

FIG. 5 is yet another embodiment of the tonometric catheter havingmultiple sensing/sampling portions;

FIG. 5A is a cross-sectional view of the tonometric catheter of FIG. 5,taken substantially along the line 5A--5A of FIG. 5;

FIG. 6 is a detailed view illustrating the tonometric catheter of FIG. 4in use within the stomach;

FIG. 7 is a detailed view illustrating the tonometric catheter of FIG. 5in use within the colon;

FIG. 8 is a similar view illustrating the tonometric catheter of FIG. 1in use within the colon;

FIG. 9 is an electrical schematic diagram illustrating one embodiment ofelectronic circuit in accordance with the invention;

FIG. 10 is an electrical schematic diagram illustrating anotherembodiment of the optical measurement of pH in accordance with theinvention;

FIG. 11 is another embodiment of a tonometric catheter with a urinarycatheter;

FIG. 11A is a cross-sectional view of the tonometric catheter/urinarycatheter of FIG. 11, taken substantially along the line IIA--IIA of FIG.11.

FIG. 12 illustrates one preferred example of the application of atonometric catheter device according to the present invention, withremote sensing and recording apparatus, for monitoring and recordingcertain critical fluid properties of interest.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a first embodiment of tonometric catheter 20. Thetonometric catheter comprises a length of suitable tubing 22, one end 32of which is closed, and the opposite end of which has a connector suchas a luer-lock 24. Luer-lock 24 is adapted to receive a complementaryfitting 26, which in turn couples through a second length of tubing 28to a three-way stopcock 30. Three-way stopcock 30 may be used toselectively connect tubing 28 to various sources of irrigation oraspiration.

Adjacent the closed end 32, tubing 22 is perforated as at 34. Aballoon-like tonometric catheter membrane 36 is fitted over the closedend so that the perforations 34 are enclosed, as illustrated. Thetonometric catheter membrane 36 has an internal sleeve diameter at 38which forms a tight fit with tubing 22. The preferred form of tonometriccatheter membrane is polydimethylsiloxane elastomer. The membrane may besealed to the tubing 22 with appropriate adhesive so that the tonometriccatheter membrane is sealed in a closed relationship to the outer wallof tubing 22, thereby forming a sampling chamber 40 adjacent closed end32. The tonometric catheter membrane has a certain elasticity to allowthe membrane to expand when filled with an aspirating liquid in order tocontact the wall of the organ under examination, as will be explainedbelow.

The membrane 36 is preferably constructed such that at least a portionof it is selectively permeable to the gas or fluid property of interest.In a preferred embodiment, it is selectively permeable to hydrogen,oxygen, or H⁺, so that pH, pCO₂ and/or pO₂ can be measured. It is alsopreferably impermeable to other materials that would interfere with thedesired measurements, such as other gases, proteins, and the like. In ahighly preferred embodiment, an ion-selective membrane is employed.

Bonded to either the inner wall or the outer wall of tubing 22 are oneor more sensors 42 for detecting a property indicative of pH and/ortemperature. Two such sensors are illustrated in FIG. 1, bonded to theoutside wall of tubing 22 with suitable adhesive. FIGS. 2A and 2Billustrate two alternate means of sensor attachment, FIG. 2Aillustrating the sensor attached to the inner wall of tubing 22 and FIG.2B illustrating the sensor attached to the outer wall of tubing 22.

In a preferred embodiment, at least a portion of the tubing, but not allof it, is made of a CO₂ impermeable material, such as polyesterelastomers derived from the reaction of dimethylterephtalate1,4-butanediol and α-hydro-ω-hydroxypoly (oxytetramethylene). In ahighly preferred embodiment, this is a material such as Hytril, sold byDuPont.

For purposes of sensing temperature, thermistor devices are presentlypreferred. For sensing properties indicative of pH chemically responsivefield effect transistors or "Chemfets" may be employed. In this regard,Chemfet sensors 44 have been illustrated in FIGS. 2A and 2B. Chemfetsensor 44 comprises a field effect semiconductor device 46, which isencapsulated in a solution impervious material 48, such as a polymerizedepoxy resin. The encapsulation material 48 in turn may be encapsulatedin a housing 50 (FIG. 2A). Semiconductor device 46 is electricallycoupled by bonding wires 52 to a terminal 54. Suitable electricalconductors such as conductor 56 are attached to terminal 54 forelectrically communicating between the Chemfet device 44 and theelectronic circuitry described below in connection with FIG. 9.Conductor 56 is preferably routed through tubing 22 and exits through asealed aperture at or near the luer-lock end of tubing 22, as at 58. Amore detailed description of a suitable electronic sensor may be foundin U.S. Pat. No. 4,020,830 to Johnson, entitled "Selective ChemicalSensitive FET Transducers," incorporated herein by reference. In orderto allow a solution to contact the chemically sensitive surface ofsemiconductor device 46, tubing 22 may be provided with an aperture 60when implementing the embodiment of FIG. 2A. Such an aperture is notneeded in the embodiment of FIG. 2B, since the semiconductor device 46is exposed to sampling chamber 40 by virtue of the external mountingconfiguration.

The sampling chamber 40 can be filled with an aspiration or samplingmedium that is used to absorb or otherwise provide a means forincorporating and delivering or measuring the the fluids or gases ofinterest. Such a medium is selected depending upon many factors,including the properties of the fluids or gases of interest, the type ofsensor 42 employed, and the type of calibration that is necessary. Suchmediums include bicarbonate solutions and saline solution. It might benoted that gases often behave as fluids and are therefore frequentlyconsidered to be fluids.

As noted above, when the sensor employed does not require frequentrecalibration, the need for the sampling chamber 40 to be incommunication with the proximate end of the tonometric catheter (thatremains outside the patient) may be eliminated since no aspiration isneeded. However, in many instances such communication may still bedesirable as aspiration may be required to calibrate the sensor orsensors, to replace the aspirating or sampling medium with a freshmedium, and to incorporate the gas or gases of interest.

Another embodiment of the tonometric catheter is illustrated in FIGS. 4,4A and 4B. As illustrated, the tonometric catheter is appropriatelyconfigured to also serve as a nasogastric sump, either with or withoutgastric suction. With reference to FIG. 4, the tonometric catheter 20acomprises a multipassage tubing 62 which defines three individualnoncommunicating (between each other) passageways or lumens, an airlumen 64, an optional suction lumen 66 and a tonometric catheter lumen68. A tonometric catheter membrane, similar to that previouslydescribed, is attached at an intermediate location on tubing 62,allowing a portion of the tubing to extend beyond the end of membrane 36to define the nasogastric sump 70. Tubing 62 is provided with aplurality of perforations 72 which communicate between tonometriccatheter lumen 68 and the sampling chamber 40 defined by membrane 36. Ifdesired, one or more sensors 42 can be included in accordance with theabove teachings, in which case a suitable conductor 56 may be routedthrough tonometric catheter lumen 68 to exit at sealed aperture 58.

The nasogastric sump portion 70 is suitably provided with a plurality ofopenings 74 through which the stomach may be aspirated.

At the opposite end of tubing 62 the tubing splits to form threeseparate connections. Air lumen 64 communicates with air lumenpassageway 76, suction lumen connects with suction lumen passageway 78and tonometric catheter lumen 68 communicates with tonometric catheterlumen passageway 80. The tonometric catheter lumen passageway is fittedwith three-way stopcock 30, similar in function and purpose to thethree-way stopcock 30 described in connection with FIG. 1. If desired, aquick connect fitting 82 may be used to couple the suction lumenpassageway 78 with an aspiration source. As illustrated, the quickconnect fitting preferably has angularly cut ends and a slightlyenlarged midsection, making it easy to insert into the end of passageway78 and also into the aspiration hose coupling (not shown). The enlargedmidsection helps form a seal with the adjoining passageways. Preferablythe quick connect fitting is fabricated of disposable plastic.

Yet another embodiment of the tonometric catheter is illustrated inFIGS. 5 and 5A. This embodiment is a multiple tonometric catheterembodiment employing a tubing 84 having a plurality of passageways orlumen as shown in the cross-sectional view of FIG. 5A. Specifically,tubing 84 includes an air lumen 86a which communicates with the endmosttonometric catheter 36a and three additional tonometric catheter lumens86b, 86c and 86d, which communicate respectively with tonometriccatheters 36b, 36c and 36d. As with the other embodiments, eachtonometric catheter may be provided with one or more sensors such assensors 42. A radiopaque tungsten plug 88 is positioned within each ofthe three tonometric catheter lumen 86b, 86c and 86d adjacent the distalend of each tonometric catheter, serving to block the remainder of thetonometric catheter lumen passageway and thereby ensuring that fluidpressure introduced into each tonometric catheter lumen will cause theassociated tonometric catheter to balloon outwardly as required duringuse. Similarly, a radiopaque tungsten rod 90 is fitted as a plug in theend of air lumen 86a, serving to terminate the end of the air lumenpassageway. Being radiopaque, the tungsten plugs and tungsten rod aid inproperly positioning the tonometric catheters by being visible underfluoroscope or x-ray. In addition, if desired, tubing 84 can be providedwith a radiopaque stripe along all or part of its length.

At the proximal end of tubing 84 the lumen 86a-86d diverge to definefour separate tubes 92a-92d. Each tube is fitted with a three-waystopcock similar to those described above. Each sampling connector mayoptionally be coded numerically by color, etc. While four approximatelyequally spaced tonometric catheters have been illustrated in FIG. 5, itwill be understood that the invention can be modified to include agreater or fewer number of tonometric catheters at different spacing asrequired for a particular application. It will also be understood thatsome or all of the tonometric catheters can include one or more sensorscoupled to conductors 56, each preferably routed through thecorresponding lumen passageway.

Referring now to FIG. 9, a suitable electronic monitoring circuit willnow be described. In FIG. 9 CHEMFET semiconductor device 46 has beenshown schematically by the equivalent circuit model enclosed in dottedlines. The device 46 thus comprises drain electrode 150, sourceelectrode 152 and reference electrode 154. The chemically selectivesystem, such as a membrane system is depicted diagrammatically at 156.The substrate is grounded as at 158.

Source electrode 154 is coupled to an input lead of operationalamplifier 160 which includes feedback network diagrammatically depictedat 162. Operational amplifier 160 senses the drain source currentflowing through device 46 and converts this signal into a voltage signalwhich is output on lead 164. The drain source current changes inaccordance with changes in the chemical system under test. Morespecifically, as the pCO₂ level changes in the fluid exposed to device46, the drain source current changes accordingly. Hence the outputvoltage signal on lead 164 is likewise an indication of the pCO₂ levelof the organ under test. This voltage signal on lead 164 is coupled toan input of comparator 166 which also receives a reference voltageV_(ref), which may be supplied using a voltage divider network (notshown) or which may alternatively be provided by a digitally controlledvoltage source 168. The output of comparator 166 is fed to referenceelectrode 154 to provide a stable reference bias voltage. If a digitallycontrolled voltage source is used, this reference voltage can beadjusted and calibrated by a computer circuit yet to be discussed. Thevoltage signal on lead 164 is also fed to an analog to digital convertor170, which is in turn coupled to a microprocessor-based microcomputer172.

In order to automatically determine the pH of the wall of the hollowviscous organ under test, a separate gas analyzer sensor 174 is used todetermine the bicarbonate concentration in the arterial blood of thepatient. The output of sensor 174 is coupled through analog to digitalconvertor 176 to microcomputer 172. Microcomputer 172 is preprogrammedto calculate the pH of the organ wall using the values provided byanalog to digital convertors 170 and 176. Conversion of pCO₂measurements can be converted into pH measurements automatically bymicrocomputer 172 using various equations and references well-known inthe art.

Although many different types of output devices may be employed, stripchart recorder 178 and CRT monitor 180 have been illustrated. Stripchart recorder 178 and monitor 180 are coupled as output devices tomicrocomputer 172. Strip chart recorder 178 offers the advantage ofdeveloping an easily readable, permanent record of the fluctuations inorgan wall pH. Monitor 180 offers the advantage of providing digitalreadout of the pH value as well as displaying the upper and lowerexcursions of pH fluctuation. If desired, microcomputer 172 can bepreprogrammed using keyboard 182 to compare the instantaneous pH valuewith doctor-selected upper and lower alarm limits. If the measuredinstantaneous pH fluctuates outside those limits, microcomputer 172 cansound an alarm to alert hospital staff.

While a single semiconductor device 46 has been illustrated inconjunction with the electronic circuit of FIG. 9, the circuit may bereadily adapted for use with a plurality of semiconductor devices inorder to measure the pH at different locations substantiallysimultaneously. In such an embodiment, the data coming from each sensorcan be fed to a separate I/0 port of microcomputer 172. In thealternative, a single I/0 port can be used with the individual inputsignals being time multiplexed.

As an alternative to electronic pH sensors, the invention may also bepracticed using optical sensor technology. Referring to FIG. 10, thepresently preferred optical sensor embodiment uses a first fiber opticcable 94 which is optically coupled through a series of lenses 96,selectable color filters 98 and heat absorber 100 to an illuminationsource 102, such as a 100 watt tungsten-halogen lamp. Fiber optic cable94 is routed through the tonometric catheter lumen in a fashion similarto the conductor 56 of the above-described embodiments, with the endthereof protruding through the tubing and into the sampling chamber 40.A second fiber optic cable 104 is routed parallel to the first fiberoptic cable 94, with one end protruding through the tubing and held inplace adjacent the end of first cable 94 with a collar 106. Collar 106may be adhesively bonded to the outside wall of the tubing. The oppositeend of second fiber optic cable 104 is positioned for optically couplingwith a phototransistor 108 which is electrically connected to anoperational amplifier circuit 110. The operational amplifier circuit canbe coupled to an analog to digital converter, such as A/D converter 170of FIG. 7.

In use, fiber optic cable 94 illuminates a region within the samplingchamber 40 which is filled with a sampling fluid containing acolorimetric pH indicator. The illumination from fiber optic cable 94reflects from the molecules suspended in the pH indicator solution, withsome of the reflected illumination passing back through second fiberoptic cable 104 to the phototransistor. By selecting the appropriatefilter 98, a monochromatic illumination or illumination of otherwiseknown spectral content is employed to illuminate the colorimetric pHindicator solution. When the color of the filtered illumination matchesthat of the indicator, the illumination is absorbed and a lowillumination signal is received at the phototransistor. When a pH changecauses a color change in the indicator away from the color of thefiltered illumination, more illumination is reflected back to thephototransistor, with an attendant increase in detected signal output.In this fashion, the proper selection of indicator dye and illuminationfiltration can be used to detect pH ranges. For a further description offiber optic pH sensor technology, refer to G. G. Vurek "A Fiber OpticpCO₂ Sensor," Annals of Biomedical Engineering, Vol. 11, pp. 499-510,1983, which is available from Pergamon Press, Ltd., and is expresslyincorporated herein by reference.

While the preferred embodiments have been disclosed in connection withmonitoring of the gastrointestinal tract and the urinary and ureterictracts it will be appreciated that its principles are applicable toother hollow internal organs to monitor pH and hence perfusion of thoseorgans. Also while several presently preferred detailed constructionsfor tonometric catheters have been disclosed, it will be appreciatedthat other constructions may be developed which are equally suitable.The disclosed constructions are presently preferred for the reason thatthey are readily fabricated using existing available materials. Otherembodiments may include other, but equivalent materials for thetonometric catheter membrane and/or connective tubing. They may alsodiffer in the specific fabrication details. As an example, the samplingchamber may be eccentric rather than symmetric about the connectivetubing.

In still another embodiment, conventional gas analyzers may be employedexternally. A device such as that shown in FIG. 1 may be used incombination with a pump or aspiration means (not shown) for continuousor regular intermittent aspiration of a sample of the aspirating liquidor medium that is used to fill the sampling chamber 40. The sampleremoved by pump or aspiration means via attachment to the luer-lock 24can be optionally designed so that the sample aspirated at each samplinginterval can be brought in contact with an exterior, separate gasanalyzing means or sensor (not shown) to determine the pH, pO₂, pCO₂and/or the like, of the sample. Such automatic sampling can be conductedemploying a system as shown in FIG. 12. In the assembly a samplingsystem employs a personal computer to conduct evaluations and analysisof the samples withdrawn from the tonometric catheter 299.

Pump 203 is loaded with the sampling or aspirating medium such assaline. Next, valve 201 is activated to withdraw a desired amount of thesampling fluid. The valve 201 is deactivated and pump 203 is used toenforce the sampling chamber of the tonometric catheter 299 using acalibrated amount or optionally a pressure transducer 215. The samplingfluid or medium is allowed to come to equilibrium with the wall of theorgan or area of interest. Next the "dead space," i.e., the area of thelumen filled with the sampling fluid that is not in equilibrium, isremoved by activating valve 205, activating pump 207, activating valve209 and infusing pump 207; the waste 21 is discarded. A sample foranalysis is then withdrawn by deactivating valve 209, activating pump207 to then deliver the sampling to a gas analyzer (not shown) thatprovides data from the sample to the PC 217, and the evaluation isconducted as described herein.

The sample gas analyzer or a separate gas analyzer may be employed todetermine the bicarbonate concentration in the arterial blood of thepatient, as described above.

Another embodiment of the tonometric catheter is illustrated in FIGS. 11and 11A. As illustrated, the tonometric catheter is appropriatelyconfigured to also serve as a urinary or ureteric catheter, either withor without suction, which optionally employs sensors. With reference toFIGS. 11 and llA, the tonometric catheter 220 comprises a multipassagetubing 262 which defines three individual noncommunicating (between eachother) passageways or lumens, an optional air or irrigation lumen 264, adrainage or suction lumen 266 and a tonometric catheter lumen 268. Atonometric catheter membrane, similar to that previously described, isattached at a distal location on tubing 262, allowing an intermediateportion of the tubing not extending beyond the end of membrane 236 todefine the uretary or uretary catheter 270. Tubing 262 is provided witha plurality of perforations 272 which communicate between tonometriccatheter lumen 268 and the sampling chamber 240 defined by membrane 236.If desired, one or more sensors 242 can be included in accordance withthe above teachings, in which case a suitable conductor 256 may berouted through tonometric catheter lumen 268 to exit at sealed aperture258.

The urinary catheter or ureteric catheter portion 270 is suitablyprovided with a plurality of openings 274 through which the bladder orureters may be aspirated or irrigated.

At the opposite end of tubing 262 the tubing splits to form threeseparate connections. Air or irrigation lumen 264 optionallycommunicates with air lumen passageway 276, urinary lumen connects withsuction or drainage lumen passageway 278 and tonometric catheter lumen268 communicates with tonometric catheter lumen passageway 280. Thetonometric catheter lumen passageway is fitted with three-way stopcock230, similar in function and purpose to the three-way stopcock 30described in connection with FIG. 1. If desired, a quick connect fitting82 as seen in FIG. 4 may be used to couple the suction urinarypassageway 278 with an aspiration source. As illustrated, the quickconnect fitting preferably has angularly cut ends and a slightlyenlarged midsection, making it easy to insert into the end of passageway278 and also into the aspiration hose coupling (not shown). The enlargedmidsection helps form a seal with the adjoining passageways. Preferablythe quick connect fitting is fabricated of disposable plastic.

Yet another embodiment of the urinary catheter/tonometric cathetercombination illustrated in FIGS. 11 and 11A may employ a multipletonometric catheter embodiment employing a tubing having a plurality ofpassageways or lumen as shown in the cross-sectional view of FIG. 5A.

In another embodiment of the present invention, a tonometric cathetermay be adopted to deliver a pharmaceutically-active agent, either forsystemic, local or topical activity, or a combination thereof. Forexample, an additional lumen may be added such as that and forirrigation or aspiration, to deliver the active. For example, theirrigation/aspiration lumen 264 shown in FIGS. 11 and 11A, may be usedto deliver an active agent. In another embodiment, a portion of thedevice may be modified so as to provide sustained release of the activeagent of interest.

Thus, for example, the problems of nosacomial infection associated withcatheter insertion can be overcome by incorporating an antimicrobialinto at least a portion of the polymeric material used to manufacturethe tonometric catheter, or by coating at least a portion of the devicewith a sustained release composition, or by delivering the antimicrobialvia the tonometric catheter. Such modifications are well known to thoseskilled in the art. See U.S. Pat. No. 4,677,143, incorporated herein byreference.

Classes of useful agents include antimicrobial agents, nonsteroidalanti-inflammatory agents, topical anesthetics, topical vasodialators,metabolic suppressants, and other agents that could be delivered forabsorption at the sites of the tonometric catheter.

Accordingly, while several preferred embodiments of the invention havebeen disclosed, it will be appreciated that principles of the invention,as set forth in the following claims, are applicable to otherembodiments.

What is claimed is:
 1. A combination tonometric catheter and urinarycatheter apparatus for measuring a liquid fluid or gaseous fluidproperty indicative of the condition of an internal organ of a human orother mammal in vivo, comprising:(a) an elongated tube having a firstlumen extending longitudinally therethrough, a portion of said tubebeing composed of a first elastomeric material that is substantiallyimpermeable to one or more liquid fluids or gaseous fluids of interest,said fluids of interest including oxygen gases and carbon dioxide gases;(b) at least one walled sampling chamber on said tube in fluidcommunication with the interior of said first lumen, the wall of saidsampling chamber being composed of a second elastomeric material that isfreely and selectively permeable to said one or more liquid fluids orgaseous fluids of interest, said second material being substantiallyimpermeable to other liquid fluids or gaseous fluids; (c) means forpositioning said walled sampling chamber substantially in direct contactwith a wall portion of said internal organ in order to allow at leastone of said liquid fluids or gaseous fluids of interest from the tissueof the wall portion of the internal organ to permeate said walledsampling chamber; and (d) a second lumen extending longitudinallythrough said tube and being adapted for the delivery or draining of afluid to or from the internal organ.
 2. An apparatus according to claim1, wherein said walled sampling chamber is defined by a balloon membercomposed of said second material generally surrounding a portion of saidtube and sealingly interconnected therewith, said balloon member beinginflated for forming an interior space between said balloon member andsaid tube and for selectively positioning a portion of said balloonmember substantially in direct contact with a wall portion of theinternal organ.
 3. An apparatus according to claim 1, wherein saidsecond lumen extends longitudinally to a distal location in the internalorgan beyond that of said first lumen and beyond that of said walledsampling chamber in order to be longitudinally spaced therefrom, saidsecond lumen including means at its longitudinally distal end forproviding fluid communication between the internal organ and theinterior of said second lumen.
 4. An apparatus according to claim 1,wherein said walled sampling chamber is resiliently inflated.